This invention relates to fluid control valves and methods, and relates more particularly to a redundant type fluid control valve capable of positively sealing the flow of a highly dangerous fluid.
Fluids such as radioactively contaminated liquids demand extremely reliable, fail-safe and long-life control valves. In nuclear power plants for instance, a flow control valve for totally shutting off the flow of a relatively high pressure, high volume flow of radioactively contaminated liquid has such rigid reliability demands. It has heretofore been the practice in such applications to provide a pair of flow shutoff valves in order to produce redundant flow shutoff capability to improve the reliability of the system. However, use of a pair of flow shutoff valves also doubles the number of modes of potential failure.
Another critical factor in the applicability of such valves is the requirement of zero leakage through the valve structure itself. It is apparent that incorporation of a pair of valves for providing redundancy also doubles the potential for such disastrous leakage.